In order to obtain a desired image an image forming apparatus such as a multi-functional peripheral charges a photoreceptor with a charging device and uses an optical scanning device to scan the photoreceptor with a light beam in accordance with image information to form an electrostatic latent image on the photoreceptor. The optical scanning device of the image forming apparatus has in its housing various lenses such as imaging lenses for focusing light on a photoreceptor from a light source emitting the light beam and various mirrors guiding the light beam to a predetermined path. Such imaging lenses making up the image forming apparatus may be acquired by the injection molding of a resin material. The imaging lenses include a long lens elongated in the main scanning direction.
Some long lenses must be positioned in a housing along with a light source, etc., to scan the photoreceptor with a light beam having desired shape/size.
Japanese Laid-Open Patent Publication No. 11-174360 discloses that when a long lens made of a resin is fixed to an optical box of an optical scanning device, positioning projections provided on the lens in the center in the longitudinal direction is engaged between two reference pins provided in the optical box to position the lens in the longitudinal direction.
Other long lenses are positioned in a housing and rotated and adjusted when used such that the long axis (longitudinal) direction thereof becomes parallel to the axis direction of a photoreceptor drum. The positioning/rotation adjustment is performed as above because the scanning positions are the same for light F scanning the near side in the axis direction and light R scanning the far side in the same direction as shown in FIG. 16A if the longitudinal direction of a long lens 1001 is parallel to the axis direction of a photoreceptor drum 1002, while the scanning positions are differentiated for the light F and the light R as shown in FIG. 16B if not parallel. If the long lens is tilted and the longitudinal direction thereof is not parallel to the axis direction of the photoreceptor drum, the optical scanning line is tilted on the image surface of the photoreceptor drum.
For the tilt adjustment of the optical scanning line on the image surface, the optical scanning device disclosed in Japanese Laid-Open Patent Publication No. 11-174360 is configured as follows. The device includes a long plastic lens having a projection formed on the bottom surface at the center portion in the longitudinal direction and supported by a V-shaped groove of the housing, and two top-surface points at both the ends in the longitudinal direction of the long plastic lens are applied to adjustment screws provided on the housing and supported by pressure. The tilt of the scanning line is corrected by loosening one of the adjustment screws and tightening the other adjustment screw, etc., to rotate and tilt the long plastic lens using the projection at the center portion as the supporting point.
However, if the positioning projection is provided in the center of the long lens as in Japanese Laid-Open Patent Publication No. 11-174360, when the lens is formed by an injection molding apparatus, a flow of a molding resin is disturbed, resulting in distortion or warpage of the imaging lens. In this case, if an optical scanning device including the lens is used in an image forming apparatus, images are distorted and image quality deteriorates.
It is desirable from a viewpoint of assembly cost that the lens is easily attached to the housing of the optical scanning device.
Since the tilt adjustment is performed with two adjustment screws at both the ends of the lens in the optical scanning device disclosed in Japanese Laid-Open Patent Publication No. 11-174360, when one end of the lens is adjusted and subsequently the opposite side is adjusted, the adjustment may not be achieved and the adjustment must be performed again although it is thought that one side is already adjusted and it is problematic that the adjustment is not easy.